The present invention relates to an automatic exposure control system for a document copying machine. More particularly, the invention relates to an exposure control system for use with a full-frame flash illumination system, which automatically compensates for the density of the background in the document to be copied.
As demands for faster copying and duplicating have increased, conventional machines which scan documents in incremental fashion to provide a flowing image on a xerographic drum have proved inadequate. New high speed techniques have evolved which utilize flash exposure of an entire document (full-frame) and the arrangement of a moving photoconductor in a flat condition at the instant of exposure. One such full-frame flash illumination system utilizing a diffuse integrating optical cavity is disclosed in copending Application of John A. Durbin and James D. Reese, Ser. No. 015,558, now U.S. Pat. No. 4,250,538, filed Feb. 26, 1979, which application is commonly assigned to the assignee of the present application. The disclosure of said application Ser. No. 015,558, now U.S. Pat. No. 4,250,538 is incorporated by reference in its entirety.